1. Field of the Invention
The present invention relates to a stage apparatus having a holder that holds a substrate as well as a stage that supports and moves the holder, an exposure apparatus comprising the stage apparatus, and an exposure method; more particularly, the present invention relates to a stage apparatus, an exposure apparatus, and an exposure method suited for use when exposing a substrate with an image of a pattern through a projection optical system and a liquid. In addition, the disclosure of the following priority application is hereby incorporated by reference in its entirety: Japanese Patent Application No. 2003-416712, filed on Dec. 15, 2003.
2. Description of the Related Art
Semiconductor devices and liquid crystal display devices are fabricated by a so-called photolithography technique, wherein a pattern formed on a mask is transferred onto a photosensitive substrate.
An exposure apparatus used in this photolithographic process comprises a mask stage that supports the mask, as well as a substrate stage that supports the substrate, and transfers the pattern of the mask onto the substrate through a projection optical system while successively moving the mask stage and the substrate stage.
There has been demand in recent years for higher resolution projection optical systems in order to handle the much higher levels of integration of device patterns. The shorter the exposure wavelength used and the larger the numerical aperture of the projection optical system, the higher the resolution of the projection optical system becomes. Consequently, the exposure wavelength used in exposure apparatuses has shortened year by year, and the numerical aperture of projection optical systems has increased. Furthermore, the mainstream exposure wavelength currently is the 248 nm KrF excimer laser, but an even shorter wavelength 193 nm ArF excimer laser is also being commercialized. In addition, as with resolution, the depth of focus (DOF) is important when performing an exposure. The following equations express the resolution R and the depth of focus δ, respectively.R=k1·λ/NA  (1)δ=±k2·λ/NA2  (2)
Therein, λ is the exposure wavelength, NA is the numerical aperture of the projection optical system, and k1 and k2 are the process coefficients. Equations (1) and (2) teach that if the exposure wavelength λ is shortened and the numerical aperture NA is increased in order to enhance the resolution R, then the depth of focus δ narrows.
At this time, if the depth of focus δ becomes excessively narrow, then it will become difficult to align the front surface of the substrate with the image plane of the projection optical system, and there will be a risk of insufficient margin during the exposure operation.
Accordingly, a liquid immersion method has been proposed, as disclosed in, for example, Patent Document 1 below, as a method to substantially shorten the exposure wavelength and increase the depth of focus. This liquid immersion method forms an immersion area by filling a liquid, such as water or an organic solvent, between the lower surface of the projection optical system and the front surface of the substrate, thus taking advantage of the fact that the wavelength of the exposure light in a liquid is 1/n of that in the air (where n is the refractive index of the liquid, normally about 1.2-1.6), thereby improving the resolution as well as increasing the depth of focus by approximately n times.
Nevertheless, the related art discussed above has the following types of problems.
The abovementioned related art is constituted so that the liquid locally fills the space between the substrate (wafer) and the end surface on the image plane side of the projection optical system, and so that the liquid does not flow out to the outer side of the substrate when exposing a shot region in the vicinity of the center of the substrate. Nevertheless, if an attempt is made to set the projection area 100 of the projection optical system to a peripheral area (edge area) E of a substrate P and then expose the edge area E of the substrate P, as depicted by the schematic diagram of FIG. 10, there is a problem in that the liquid flows out to the outer side of the substrate P, and therefore the immersion area does not form satisfactorily, which degrades the projected pattern image. In addition, the liquid that flows out can also cause problems such as rusting of mechanical parts and the like around the substrate stage that supports the substrate P, as well as electrical leakage of the stage drive system and the like.
Furthermore, if the liquid that flows out to the outer side of the substrate P travels around to the rear surface of the substrate P and infiltrates the space between the substrate P and the substrate stage (substrate holder), then it will also cause a problem wherein the substrate stage cannot satisfactorily hold the substrate P. In addition, if the liquid infiltrates the step or the gap between the substrate P and the substrate stage, then in this case as well there is a possibility that the liquid will cause rust or electric leakage. Particularly if a positioning notched part, such as a notched part and an orientation flat part (orientation flat), is formed in the substrate P, then the gap between the outer circumference of the substrate P and the table part at the periphery thereof will increase, which will consequently make it easy for the liquid to travel around through this gap.
The present invention was made considering the abovementioned problems, and it is an object of the present invention to provide a stage apparatus, an exposure apparatus, and an exposure method that can prevent the infiltration of a liquid into the space between a substrate and a holder, and that can perform exposure in a state wherein an immersion area is satisfactorily formed, even when exposing an edge area of the substrate.